Lithographic apparatus and device manufacturing method

ABSTRACT

A substrate table of an immersion lithographic apparatus is disclosed which comprises a barrier configured to collect liquid. The barrier surrounds the substrate and is spaced apart from the substrate. In this way any liquid which is spilt from the liquid supply system can be collected to reduce the risk of contamination of delicate components of the lithographic projection apparatus.

FIELD

The present invention relates to a lithographic apparatus and a devicemanufacturing method.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a target portion of a substrate. Lithographic apparatus can beused, for example, in the manufacture of integrated circuits (ICs). Inthat circumstance, a patterning device, such as a mask, may be used togenerate a circuit pattern corresponding to an individual layer of theIC, and this pattern can be imaged onto a target portion (e.g.comprising part of, one or several dies) on a substrate (e.g. a siliconwafer) that has a layer of radiation-sensitive material (resist). Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively exposed. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through the projection beam in a given direction(the “scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective NA of the system and alsoincreasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see, for example, U.S. Pat. No. 4,509,852, herebyincorporated in its entirety by reference) means that there is a largebody of liquid that must be accelerated during a scanning exposure. Thismay require additional or more powerful motors and turbulence in theliquid may lead to undesirable and unpredictable effects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate using a liquidsupply system (the substrate generally has a larger surface area thanthe final element of the projection system). One way which has beenproposed to arrange for this is disclosed in PCT patent applicationpublication no. WO 99/49504, hereby incorporated in its entirety byreference. As illustrated in FIGS. 2 and 3, liquid is supplied by atleast one inlet IN onto the substrate, preferably along the direction ofmovement of the substrate relative to the final element, and is removedby at least one outlet OUT after having passed under the projectionsystem. That is, as the substrate is scanned beneath the element in a −Xdirection, liquid is supplied at the +X side of the element and taken upat the −X side. FIG. 2 shows the arrangement schematically in whichliquid is supplied via inlet IN and is taken up on the other side of theelement by outlet OUT which is connected to a low pressure source. Inthe illustration of FIG. 2 the liquid is supplied along the direction ofmovement of the substrate relative to the final element, though thisdoes not need to be the case. Various orientations and numbers of in-and out-lets positioned around the final element are possible, oneexample is illustrated in FIG. 3 in which four sets of an inlet with anoutlet on either side are provided in a regular pattern around the finalelement.

Having immersion liquid inside the lithographic apparatus may presentproblems if the liquid is permitted to contaminate sensitive parts ofthe apparatus. This is particularly the case with a localized arealiquid supply system because if such a liquid supply system fails,immersion liquid can easily escape. Furthermore, if the localized arealiquid supply system is not efficient, immersion liquid can be leftbehind on the substrate table and then can leave the substrate tableunder the forces generated by the acceleration of the substrate table.

SUMMARY

Accordingly, it would be advantageous, for example, to reduce the riskof contamination with liquid of components in an immersion lithographicprojection apparatus.

According to an aspect, there is provided a lithographic apparatuscomprising:

-   -   an illuminator configured to provide a beam of radiation;    -   a support structure configured to hold a patterning device, the        patterning device configured to impart the beam with a pattern        in its cross-section;    -   a substrate table configured to hold a substrate;    -   a projection system configured to project the patterned beam        onto a target portion of the substrate; and    -   a liquid supply system configured to supply a liquid to a        localized area of the substrate, the substrate table or both to        at least partly fill a space between the projection system and        the substrate, the substrate table or both,    -   wherein the substrate table comprises a barrier configured to        collect liquid, the barrier surrounding and spaced apart from        the substrate.

Using the barrier, liquid spilt by the liquid supply system or escapingfrom the liquid supply system may be collected and recycled or disposedof without components in the apparatus being contaminated with theescaped liquid. The barrier need not take up very much space on thesubstrate table. This is advantageous because space is limited on thesubstrate table which is made as small as possible so that an as smallas possible mass needs to be accelerated.

In an embodiment, the barrier comprises a projection which projects outof an upper surface of the substrate table. This is a simple physicalbarrier to prevent liquid from flying off the substrate table due toforces generated by the acceleration of the substrate table or becauseof catastrophic failure of the liquid supply system (e.g., according toany of the solutions described herein).

In an embodiment, at least a part of the barrier comprises aliquidphillic material or coating. Constructing the barrier of such amaterial or apply such a coating to the barrier enhances collection ofliquid, which sticks to the barrier.

In an embodiment, the barrier comprises a groove recessed into an uppersurface of the substrate table. This has an advantage that thecross-sectional profile of the substrate table has an upper surfacewhich is generally level with an upper surface of the substrate. It isthen not necessary to move the substrate table or the liquid supplysystem in the direction of the optical axis of the projection system toavoid collisions between the substrate table and the liquid supplysystem and/or the projection system, for example, during substrate swap.

In an embodiment, the groove is sized such that liquid can betransported along the groove under capillary action. Such sizing canfacilitate transportation of liquid collected by the barrier to a lowpressure supply configured to remove liquid from the barrier, withoutthe need of any additional components. The substrate table may comprisea chamber in liquid contact with the upper surface via the groove. Thegroove may be made continuous. Using the chamber, the vacuum flow over alength of the groove may be equalized. In an embodiment, this may thenrequire the use of a only few discrete outlets.

In an embodiment, a low pressure supply may be provided to remove liquidfrom the barrier. The low pressure supply may comprise individualdiscrete low pressure outlets, which may be provided to the groove orthe chamber.

In an embodiment, the low pressure supply operates independently of theliquid supply system. In this way, in case of failure of the liquidsupply system and therefore overflow of liquid, the barrier can stilloperate.

A way of transporting liquid along the barrier is to provide an acousticwave generator configured to generate surface acoustic waves in thebarrier. In an embodiment, this can be provided by the use of apiezoelectric actuator, which may advantageously be made quite small.

In an embodiment, the barrier comprises a groove and a projection whichprojects out of an upper surface of the substrate table. An advantage ofthis combination is, for example, that liquid with a high speed alongthe upper surface of the substrate table can be removed. The projectionessentially acts as a dam and as liquid builds up against the dam itwill be drained away via the groove. In combination with a chamber,which optionally may be at least partly formed in the projection, inliquid contact with the upper surface via the groove, a particularlyeffective barrier can be formed.

In an embodiment, the barrier is positioned radially outwardly of adrainage ditch or barrier surrounding an outer peripheral edge of thesubstrate. Such a drainage ditch or barrier surrounding an outerperipheral edge of the substrate is provided so that when edge portionsof the substrate are being exposed and the localized area liquid supplysystem supplies liquid to areas both on the substrate and the substratetable simultaneously, the amount of liquid which escapes through the gapbetween the substrate and the substrate table is reduced. Examples of adrainage ditch or barrier surrounding an outer peripheral edge of thesubstrate can be found, for example, in U.S. patent application Ser. No.10/705,804, hereby incorporated in its entirety by reference. Liquidwhich happens to escape the drainage ditch or barrier may be collectedby the barrier. The barrier extends essentially around an outer edge orportion of the substrate table. Thus, with any relative position of theliquid supply system on the substrate table, the barrier can be used tocollect liquid which is spilled. The barrier can additionally surroundareas of an upper surface of the substrate table which are not coveredby the substrate. Also, the barrier may additionally surround at leastone sensor mounted on an upper surface of the substrate table and/or aclosure member configured to seal the liquid supply system. The sensormay be a transmission image sensor used in alignment. The closure membermay be in the form of a disk designed to be connected to the bottom ofthe liquid supply system to contain liquid in the liquid supply system,for example, during substrate swap after exposure of one substrate andbefore exposure of a following substrate. A typical example of a closuremember is disclosed in U.S. patent application Ser. No. 10/705,785,hereby incorporated in its entirety by reference.

According to a further aspect, there is provided a device manufacturingmethod comprising:

-   -   providing a liquid to a localized area of a substrate, a        substrate table or both to at least partly fill a space between        a projection system and the substrate, the substrate table or        both;    -   projecting a patterned beam of radiation through the liquid onto        a target portion of the substrate using the projection system;        and    -   collecting liquid with a barrier, the barrier surrounding and        spaced apart from the substrate.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,liquid-crystal displays (LCDs), thin-film magnetic heads, etc. Theskilled artisan will appreciate that, in the context of such alternativeapplications, any use of the terms “wafer” or “die” herein may beconsidered as synonymous with the more general terms “substrate” or“target portion”, respectively. The substrate referred to herein may beprocessed, before or after exposure, in for example a track (a tool thattypically applies a layer of resist to a substrate and develops theexposed resist) or a metrology or inspection tool. Where applicable, thedisclosure herein may be applied to such and other substrate processingtools. Further, the substrate may be processed more than once, forexample in order to create a multi-layer IC, so that the term substrateused herein may also refer to a substrate that already contains multipleprocessed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of 365, 248, 193, 157 or 126 nm).

The term “patterning device” used herein should be broadly interpretedas referring to a device that can be used to impart a projection beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the projection beam may not exactly correspond to thedesired pattern in the target portion of the substrate. Generally, thepattern imparted to the projection beam will correspond to a particularfunctional layer in a device being created in the target portion, suchas an integrated circuit.

A patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions; in this manner, thereflected beam is patterned. In each example of a patterning device, thesupport structure may be a frame or table, for example, which may befixed or movable as required and which may ensure that the patterningdevice is at a desired position, for example with respect to theprojection system. Any use of the terms “reticle” or “mask” herein maybe considered synonymous with the more general term “patterning device”.

The term “projection system” used herein should be broadly interpretedas encompassing various types of projection system, including refractiveoptical systems, reflective optical systems, and catadioptric opticalsystems, as appropriate for example for the exposure radiation beingused, or for other factors such as the use of an immersion fluid or theuse of a vacuum. Any use of the term “lens” herein may be considered assynonymous with the more general term “projection system”.

The illumination system may also encompass various types of opticalcomponents, including refractive, reflective, and catadioptric opticalcomponents for directing, shaping, or controlling the projection beam ofradiation, and such components may also be referred to below,collectively or singularly, as a “lens”.

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIG. 2 illustrates, in cross-section, a liquid supply system which maybe used in accordance with the present invention;

FIG. 3 illustrates, in plan, the liquid supply system of FIG. 2;

FIG. 4 illustrates an example of a liquid supply system seal memberaccording to an embodiment of the invention;

FIG. 5 illustrates, in cross-section, a barrier according to a firstembodiment of the invention;

FIG. 6 illustrates, in plan, a barrier according to a second embodimentof the invention;

FIG. 7 illustrates, in cross-section, a barrier according to a thirdembodiment of the invention; and

FIG. 8 illustrates, in cross-section, a barrier according to a fourthembodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to aparticular embodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL for providing a        projection beam PB of radiation (e.g. UV radiation).    -   a first support structure (e.g. a mask table) MT for supporting        a patterning device (e.g. a mask) MA and connected to a first        positioning device PM for accurately positioning the patterning        device with respect to item PL;    -   a substrate table (e.g. a wafer table) WT for holding a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioning device for accurately positioning the        substrate with respect to item PL; and    -   a projection system (e.g. a refractive projection lens) PL for        imaging a pattern imparted to the projection beam PB by the        patterning device MA onto a target portion C (e.g. comprising        one or more dies) of the substrate W.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above).

The illuminator IL receives a beam of radiation from a radiation source.The source and the lithographic apparatus may be separate entities, forexample when the source is an excimer laser. In such cases, the sourceis not considered to form part of the lithographic apparatus and theradiation beam is passed from the source to the illuminator IL with theaid of a beam delivery system comprising for example suitable directingmirrors and/or a beam expander. In other cases the source may beintegral part of the apparatus, for example when the source is a mercurylamp. The source and the illuminator IL, together with the beam deliverysystem if required, may be referred to as a radiation system.

The illuminator IL may comprise adjusting means AM for adjusting theangular intensity distribution of the beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator ILgenerally comprises various other components, such as an integrator INand a condenser CO. The illuminator provides a conditioned beam ofradiation, referred to as the projection beam PB, having a desireduniformity and intensity distribution in its cross-section.

The projection beam PB is incident on the mask MA, which is held on themask table MT. Having traversed the mask MA, the projection beam PBpasses through the lens PL, which focuses the beam onto a target portionC of the substrate W. With the aid of the second positioning device PWand position sensor IF (e.g. an interferometric device), the substratetable WT can be moved accurately, e.g. so as to position differenttarget portions C in the path of the beam PB. Similarly, the firstpositioning device PM and another position sensor (which is notexplicitly depicted in FIG. 1) can be used to accurately position themask MA with respect to the path of the beam PB, e.g. after mechanicalretrieval from a mask library, or during a scan. In general, movement ofthe object tables MT and WT will be realized with the aid of along-stroke module (coarse positioning) and a short-stroke module (finepositioning), which form part of the positioning devices PM and PW.However, in the case of a stepper (as opposed to a scanner) the masktable MT may be connected to a short stroke actuator only, or may befixed. Mask MA and substrate W may be aligned using mask alignment marksM1, M2 and substrate alignment marks P1, P2.

The depicted apparatus can be used in the following preferred modes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to theprojection beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the projection beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the masktable MT is determined by the (de-)magnification and image reversalcharacteristics of the projection system PL. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the projection beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as required after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizes aprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

A first embodiment of the invention is described with reference to FIG.5. A substrate table WT which supports a substrate W is illustrated. Thesubstrate table WT may be any sort of substrate table including the typewhich comes in an upper and a lower part wherein the lower part movesrelative to the apparatus and is designed for coarse positionalmovements and the upper part moves relative to the lower part and isdesigned for accurate “short-stroke” positioning. Further, the substratetable WT may be one of the type where a chuck is releasably attachableto the substrate table WT and supported by the substrate table WT. Inthe following description, no distinction shall be made between thedifferent types of substrate table WT and the description of thesubstrate table WT will be generic.

A substrate table WT used in immersion lithography may be provided witha drainage ditch or barrier 40 surrounding an outer peripheral edge ofthe substrate W. The drainage ditch or barrier 40 is connected to a lowpressure source such that immersion liquid spilt from the substrate Wduring exposure of edge portions of the substrate W can be retrieved.Examples of such a drainage ditch or barrier 40 can be found in U.S.patent application Ser. No. 10/705,804, hereby incorporated in itsentirety by reference.

Further, other objects 20 are positioned on an upper surface of thesubstrate table which is substantially in the same plane as the uppersurface of the substrate W. The other objects 20 may include sensors 24(including, for example, a transmission image sensor (TIS) and/or a spot(dose) sensor) or a so-called closing disk 22 as shown in FIG. 6. Atransmission image sensor 24 is used during alignment of the substrate Wrelative to the substrate table WT and is typically illuminated by aprojection beam PB through the projection system. A closing disk 22 istypically used during substrate swap. After a substrate has beenexposed, it is removed from the substrate table WT and replaced by anew, non-exposed substrate W. During this period it may be advantageousto maintain a final element of the projection system immersed in liquidto avoid drying marks on the final element. To this end, a closing disk22 is provided which can be connected to the underside of the liquidsupply system so that the liquid supply system may be maintainedoperational without catastrophic loss of liquid. A closing disk isdescribed in more detail in U.S. patent application Ser. No. 10/705,785,hereby incorporated in its entirety by reference.

A barrier 100 surrounds the substrate W, the drainage ditch 40 and theclosing disk 22 and the transmission image sensor 24. The barrier 100also surrounds other areas of the upper surface of the substrate tableWT. The barrier 100 is continuous and is positioned substantially at anouter edge or portion of the upper surface of the substrate table WT.The barrier 100 is physically out of the plane of the upper surface ofthe substrate table WT (and substrate W). For the type of substratetable WT which comprises a substrate chuck as well as the table, thebarrier 100 may either be positioned around the outside of the chuck oraround the outside of the substrate table.

In the first embodiment, the barrier 100 comprises a groove 110 which isrecessed into the upper surface of the substrate table WT. The groove110 is a continuous loop (whether circular or non-circular) but need notbe. The groove 110 may be accompanied by a projection 140 which projectsabove the upper surface of the substrate table WT. In an embodiment, theprojection 140 is positioned radially outwardly of the groove 110. A lowpressure supply is attached to a plurality of discrete outlets 120. Thediscrete outlets 120 are connected to the low pressure supply, which is,in an embodiment, independent of the liquid supply system so that anyliquid which is collected by the barrier 100 can be removed for disposalor optionally for recycling. In an embodiment, the outlet 120 may be acontinuous loop (whether circular or non-circular).

The barrier 100 is advantageously made of a liquidphillic material orhas a liquidphillic coating such that any liquid which comes intocontact with the barrier 100 is attracted to the barrier 100 which canthen work more effectively in collecting the liquid.

In an embodiment, the groove 100 is formed as a U-shape in cross-sectionand is sized such that capillary forces act on liquid in the groove sothat the liquid can be transported to the outlet(s) 120 and removed fromthe substrate table WT.

An alternative for the transport of liquid along the barrier 100 is togenerate surface acoustic waves which are a time-varying deformation orvibration on the surface and/or just below the surface of the barrier(e.g., a groove). The liquid is transported by the time varyingdeformation of the surface. The surface acoustic waves can be generatedby a surface acoustic wave generator which may comprise piezoelectricactuators. This design is very compact and the surface acoustic wavescan be generated very locally on the surface. Therefore, the surfaceacoustic waves will only run along the surface of the material of thebarrier 100 so that no mechanical distortion of the substrate table (orchuck) occurs.

A second embodiment is described with reference to FIG. 6 and is thesame as the first embodiment except as described below. In thisembodiment, two collecting recesses 122 are provided at opposite cornersof the barrier 100. The collecting recesses 122 are semi-spherical inshape and have at their deepest recessed point an outlet 120. The groove110 may be slightly tilted along its length such that any liquid in thegroove 110 will run under force of gravity towards the collectingrecesses 122. Of course, the groove 110 may be sized such that capillaryforces move the liquid towards the collecting recesses 122 or a surfaceacoustic wave generator may be employed for this purpose.

A third embodiment is described with reference to FIG. 7 and is the sameas the first embodiment except as described below. In this embodiment,the barrier 100 comprises a continuous groove 110 extending around anouter edge or portion of the substrate table WT. The continuous groove110 is in fluid communication with a continuous annular chamber 130formed in the substrate table and which has a cross-sectional arealarger than that of the groove. A plurality of discrete outlets 120 (ora single continuous outlet 120), which are connected to a low pressuresource, are in fluid communication with the chamber 130. In this way,the under pressure in the groove 110 is equalized along its entirelength so that the force which forces liquid into the drainage system isequal along the whole length of the barrier 100.

As in other embodiments but in contrast to the drainage ditch 40, thebarrier 100 is spaced apart from the substrate W when the substrate W ispositioned on the substrate table WT in the area designated for asubstrate W.

A fourth embodiment is the same as the third embodiment except asdescribed below with reference to FIG. 8. The fourth embodiment isdesigned, for example, to optimize removal of liquid which has a highvelocity on the upper surface of the substrate table WT. Liquid mightdevelop a high velocity on the substrate table when the substrate tablemoves with high speed in the plane orthogonal to the optical axis of theprojection system.

The barrier 100 of the fourth embodiment comprises a projection 140which projects above the upper surface of the substrate table WT andextends around an outer edge or portion of the substrate table WTsubstantially at the outer edge or portion of the substrate table WT. Agroove 110 is formed in the projection 140. The groove 110 extendshorizontally substantially parallel to the upper surface of thesubstrate table WT in contrast to the grooves of the foregoingembodiments which are substantially perpendicular to the upper surfaceof the substrate table WT. However, in the fourth embodiment, as withthe other embodiments, the groove 110 may make any angle with the uppersurface of the substrate table WT. The horizontal angle of the groove10, in the fourth embodiment, is preferred because when liquid is forcedup against the radially inner surface of the projection 140,acceleration of the substrate table WT from the left to right asillustrated in FIG. 8 results in a force on the liquid which will beeffective to force the liquid through the groove 110.

The inner surface of the projection 140 is illustrated as beingperpendicular to the upper surface of the substrate table WT. This isperhaps the easiest shape to machine though an angle which results inthe projection 140 overhanging the upper surface of the substrate tableWT (i.e. angled inwardly) may be advantageous as liquid is then lesslikely to be forced over the top of the projection 140 as liquid buildsup against the radially inner surface.

The chamber 130 of the fourth embodiment is formed at least partly inthe projection 140. This need not necessarily be the case but it doesmake manufacture easier. In fact, the chamber 130 may be entirely formedwithin the projection 140. In this way the barrier 100 may be formed,for example, of an annular ring with a cross-sectional shape of a Uwhich is glued or otherwise attached to the upper surface of thesubstrate table WT. As will be apparent, other shapes and cross-sectionsare possible.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

Another immersion lithography solution which has been proposed is toprovide the liquid supply system with a seal member which extends alongat least a part of a boundary of the space between the final element ofthe projection system and the substrate table. The seal member issubstantially stationary relative to the projection system in the XYplane though there may be some relative movement in the Z direction (inthe direction of the optical axis). A seal is formed between the sealmember and the surface of the substrate. Preferably the seal is acontactless seal such as a gas seal. Such a system is disclosed in, forexample, U.S. patent application Ser. No. 10/705,783, herebyincorporated in its entirety by reference.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

In European patent application no. 03257072.3, hereby incorporated inits entirety by reference, the idea of a twin or dual stage immersionlithography apparatus is disclosed. Such an apparatus is provided withtwo substrate tables for supporting the substrate. Leveling measurementsare carried out with a substrate table at a first position, withoutimmersion liquid, and exposure is carried out with a substrate table ata second position, where immersion liquid is present. Alternatively, theapparatus can have only one substrate table moving between the first andsecond positions.

The present invention can be applied to any immersion lithographyapparatus, in particular, but not exclusively, to those types mentionedabove.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. The description is not intended to limit theinvention.

1. A lithographic apparatus comprising: an illuminator configured to provide a beam of radiation; a support structure configured to hold a patterning device, the patterning device configured to impart the beam with a pattern in its cross-section; a substrate table configured to hold a substrate; a projection system configured to project the patterned beam onto a target portion of the substrate; and a liquid supply system configured to supply a liquid to a localized area of the substrate, the substrate table or both to at least partly fill a space between the projection system and the substrate, the substrate table or both, wherein the substrate table comprises a barrier configured to collect liquid, the barrier surrounding and spaced apart from the substrate.
 2. The apparatus of claim 1, wherein the barrier comprises a projection which projects out of an upper surface of the substrate table.
 3. The apparatus of claim 1, wherein at least a part of the barrier comprises a liquidphillic material or coating.
 4. The apparatus of claim 1, wherein the barrier comprises a groove recessed into an upper surface of the substrate table.
 5. The apparatus of claim 4, wherein the groove is sized such that the liquid can be transported along the groove under capillary action.
 6. The apparatus of claim 4, wherein the substrate table further comprises a chamber in liquid contact with the upper surface via the groove and wherein the groove forms a continuous loop.
 7. The apparatus of claim 1, further comprising a low pressure supply configured to remove liquid from the barrier.
 8. The apparatus of claim 7, wherein the low pressure supply comprises a plurality of discrete outlets.
 9. The apparatus of claim 7, wherein the low pressure supply operates independently of the liquid supply system.
 10. The apparatus of claim 1, further comprising a surface acoustic wave generator configured to generate surface acoustic waves in the barrier to facilitate transport of liquid along the barrier.
 11. The apparatus of claim 10, wherein the surface acoustic wave generator comprises a piezoelectric actuator.
 12. The apparatus of claim 1, wherein the barrier comprises a groove and a projection which projects out of an upper surface of the substrate table.
 13. The apparatus of claim 12, wherein the substrate table comprises a chamber in liquid contact with the upper surface via the groove.
 14. The apparatus of claim 13, wherein the chamber is at least partly formed in the projection.
 15. The apparatus of claim 1, wherein the barrier is positioned radially outwardly of a drainage ditch or barrier surrounding an outer peripheral edge of the substrate.
 16. The apparatus of claim 1, wherein the barrier extends substantially around an outer edge or portion of the substrate table.
 17. The apparatus of claim 1, wherein the barrier additionally surrounds areas of an upper surface of the substrate table which are not covered by the substrate.
 18. The apparatus of claim 1, wherein the barrier additionally surrounds at least one sensor mounted on an upper surface of the substrate table and/or a closure member configured to seal the liquid supply system.
 19. A device manufacturing method comprising: providing a liquid to a localized area of a substrate, a substrate table or both to at least partly fill a space between a projection system and the substrate, the substrate table or both; projecting a patterned beam of radiation through the liquid onto a target portion of the substrate using the projection system; and collecting liquid with a barrier, the barrier surrounding and spaced apart from the substrate.
 20. The method of claim 19, wherein the barrier comprises a projection which projects out of an upper surface of the substrate table.
 21. The method of claim 19, wherein the barrier comprises a groove recessed into an upper surface of the substrate table.
 22. The method of claim 19, further comprising removing liquid from the barrier using a low pressure supply.
 23. The method of claim 22, wherein removing liquid from the barrier operates independently of providing the liquid.
 24. The method of claim 19, further comprising generating surface acoustic waves in the barrier to facilitate transport of liquid along the barrier.
 25. The method of claim 19, wherein the barrier comprises a groove and a projection which projects out of an upper surface of the substrate table.
 26. The method of claim 25, wherein the substrate table comprises a chamber at least partly formed in the projection and in liquid contact with the upper surface via the groove.
 27. The method of claim 19, further comprising removing liquid using a drainage ditch or barrier surrounding an outer peripheral edge of the substrate and positioned radially inwardly of the barrier. 